454 



NA TURE 



[September 6, 1900 



definitions given we note a frequent lack of accuracy and 

 precision, as, for example, with that of the Ophidia as 

 having their "eyelids absent." The senior author's pre- 

 vious work explains the introduction of experimental 

 observations of the antenniform-ophthalmite order, and 

 brief note is taken of " variation " and abnormality. The 

 social life and " language " of ants, protective resemblance 

 and mimicry among the Lepidoptera, the habits of the 

 spiders, and many other similarly fascinating topics 

 receive in due course passing consideration. The reader 

 will put down the book feeling the better for its perusal 

 and with a desire to know more, while its " keys" to the 

 identification of the common forms of life, oft overlooked 

 because always present, but withal foremost in their 

 claims on our attention, will prove useful and encouraging. 

 We are doubtful, however, whether the authors would not 

 have done better to have attempted less and that more 

 uniformly, and whether they are justified in their refrain 

 that in matters of elementary scientific education the 

 mere " needs " of the ordinary citizen are to be alone 

 gratified. We are by no means convinced that this 

 argument is sound. Their method would seem likely 

 to discount the teacher's important function of deciding 

 what is to be left untaught — a matter of the utmost 

 urgency in elementary scientific work. We shall watch 

 with interest the development of their scheme. 



COLOUR PHOTOGRAPHY. 

 A Handbook of Photography in Colours. By Thomas 

 Bolas, Alexander A. K. Tallent and Edgar Senior. 

 Pp. viii + 343. (London : Marion and Co., 1900.) 



THE preface or introduction is written by the 

 publishers, and is immediately followed by an 

 index. Then follow three "sections." (i ) 85 pages, 

 by Mr. Bolas, on the " Historical Development of Helio- 

 chromy. General Survey of Processes. Direct Helio- 

 chromes on Silver Chloride." (2) 205 pages, by Mr. 

 Tallent, on " Three-colour Photography." (3) 27 pages 

 by Mr. Senior, on " Lippmann's Process of Interference 

 Heliochromy." Each section is quite distinct from the 

 others, except that they are bound into one volume and 

 indexed together ; there is therefore much repetition. 

 For example. Maxwell's colour-sensation curves and 

 Abney's revised curves are each given twice (the two 

 renderings, by the way, are not identical), and Lipp- 

 mann's formula for his emulsion is given at p. 55 and also 

 at p. 332. Careful editing would have avoided such 

 waste of space. Some of the diagrams are drawn with 

 exceedingly thick lines, and are provided with very large 

 heavy lettering, while others incline rather in the oppo- 

 site direction. Some of the spectra as drawn for showing 

 absorption, sensitiveness and so on, have the red to the 

 left-, and others the red to the right-hand side ; some are 

 normal, and others are as produced by prisms. It may 

 be said that these are quoted from various sources ; but 

 in a volume in which it is thought necessary to explain 

 with a large diagram the refraction of light on passing 

 from air into water, surely a little explanation of these 

 differences is desirable. At p. 180, a spectrum which is 

 normal is described as " prismatic." The volume appears 

 not to have been edited at all, therefore the only way to 

 NO. 1610, vol. 62] 



do justice to the authors is to regard it as three distinct 

 books. 



Mr. Bolas gives an excellent summary of the whole 

 subject, both historical and practical. As a careful com- 

 piler should do, he has erred, if it be an error, in including 

 too much rather than too little. Carey Lea's highly 

 coloured partial reduction products of the halogen salts 

 of silver might have been passed by, by some writers, as 

 well as other references to conjectures. Zenker's work 

 and Wiener's investigations are described intelligibly, 

 although concisely ; indeed, the author has evidently 

 spared no pains to give every one his due, and to use to 

 the best advantage the small space at his disposal. 



Mr. Tallent begins his section with several pages on 

 the properties of light and the construction of ordinary 

 spectroscopes — matter which, we think, might well have 

 been omitted in order to make room for the treatment of 

 subjects for which the reader is often referred to other 

 books or articles. The peculiar firework-like diagram at 

 p. 112, given to illustrate dispersion, is more likely to 

 mislead than assist the student ; and some of the other 

 diagrams might have been made more clear, in spite of 

 the extraordinary boldness of the drawing and lettering. 

 Mr. Tallent has gathered together a great deal of in- 

 formation about three-colour work, which he presents in 

 the form of notes rather than as a treatise. It is doubt- 

 less advantageous in some cases to supply the raw 

 material only, but the possession of bricks and mortar 

 does not enable every one to build himself a house. If 

 the very popular style of description sometimes adopted 

 were given up in favour of more technical details, and 

 if the practical applications of the various principles 

 were more closely associated with the enunciation of the 

 principles themselves, we think that the book would be 

 more useful to the large majority of those who will read it. 

 But we must be grateful to Mr. Tallent for having made 

 a beginning in the getting together of the hitherto widely 

 scattered items of the subject. His work must be of con- 

 siderable assistance to any one following him, and we 

 hope -that later on he himself may be able to give us a 

 treatise founded on these notes. 



Mr. Senior treats only of Lippmann's interference 

 process, and he writes on this with authority, for he has 

 given the matter much practical attention, and has pro- 

 duced some of the best examples that have been seen. 

 He gives his formuUe and methods apparently without 

 any reserve, as well as the published formulas of other 

 notable workers. He precedes the practical details with 

 a few pages on the optical principles involved, setting 

 forth clearly the character of " stationary waves." We 

 think that most people reading p. 323 would consider it 

 as showing that the colours reflected from a Lippmann 

 photograph are complementary to those of the objects 

 photographed, but it is quite obvious that Mr. Senior does 

 not intend to convey this impression. 



The publishers, in their preface, state that thirty-one 

 years ago they published the pioneer work on photo- 

 graphy in colours (by Ducos du Hauron), and they feel 

 satisfaction now in following up the line they " opened up 

 over a quarter of a century ago." All who are interested 

 in the subject will feel thankful to Messrs. Marion and Co. 

 for having done so. C. J. 



